The Katyn massacre, carried out by the Soviet NKVD in 1940, was only one of many unspeakable crimes committed by Stalin's ruthless executioners over three decades. The mass murder of thousands of Polish officers was part of a relentless purge, the secrets and details of which have only recently been partially revealed.
Lavrentiy Pavlovich Beria (29 March [O.S. 17 March] 1899 – 23 December 1953) was a Georgian Bolshevik and Soviet politician, Marshal of the Soviet Union and state security administrator, chief of the Soviet security, and chief of the People's Commissariat for Internal Affairs (NKVD) under Joseph Stalin during World War II, and promoted to deputy premier under Stalin from 1941. He later officially joined the Politburo in 1946. Description above from the Wikipedia article Lavrentiy Beria, licensed under CC-BY-SA, full list of contributors on Wikipedia.